1. Field of the Invention
The present invention generally relates to an automotive engine system and, more particularly, to an engine balancer used to minimize vibrations occurring in the engine system.
2. Description of the Prior Art
The use of an engine balancer in an automotive engine construction is well known. In general, one or more balancer shafts each having a balance weight are provided in an engine cylinder block and are drivingly coupled with a power output shaft of the engine so that the balancer shafts can be driven at a number of revolution per unit time which is equal to, or an integral multiple of, that of the engine power output shaft so as to produce centrifugal forces necessary to counteract first-harmonic, second-harmonic or higher-harmonic moments and/or inertia forces which have resulted from the reciprocating motion of the pistons within the engine cylinders.
When it comes to the balancer shafts, some methods of installing the balancer shafts in the engine system are well known. One method is that a generally elongated balancer chamber for each of the balancer shafts is defined in the cylinder block in parallel relationship with the crankshaft and the respective balancer shaft is operatively supported in position inside the balancer chamber with its opposite end rotatably extending outwardly through the front and rear end walls of the cylinder block, such as disclosed in, for example, the U.S. Pat. No. 4,028,963, patented June 14, 1977. Another method is that the balancer shafts are disposed inside the crankcase while suspended from the bottom of the cylinder block, such as disclosed in, for example, the Japanese Laid-open Patent Publication No. 58-160645 published Sept. 24, 1983.
According to the first-mentioned publication, the support rigidity of the balancer shafts is high and a drive mechanism for driving the balancer shafts can be employed which is similar in construction to that used for driving auxiliary equipments. However, since the balancer shafts extend completely through the engine cylinder block and lengthwise of the engine itself, and since the front ends of the balancer shafts situated outside and adjacent the front end wall of the engine cylinder block are drivingly coupled with a belt type or gear type drive mechanism, not only is the installation of the balancer shafts in the engine system complicated and time-consuming, but also the engine must have a substantial length to accommodate one or more drive belts for driving the auxiliary equipments and the drive mechanism for the balancer shafts that are arranged offset one after another in a direction lengthwise of the engine. While the drive mechanism for the balancer shafts may be either a combination of an endless belt and pulleys, a combination of an endless chain and sprocket wheels, or a train of gears, an additional problem would occur where the endless chain or the gear train is employed, for it requires a regular oiling.
According to the second-mentioned publication, a train of gears necessitated to transmit the drive of the engine power output shaft to the balancer shafts is disposed exteriorly of the rear end wall of the engine cylinder block and, therefore, any possible interference between the drive mechanism for the balancer shafts and those for the auxiliary equipments such as occurring in the method according to the first-mentioned publication can be avoided.
However, even the method of the second-mentioned publication has problems. Specifically, not only is the support rigidity of the balancer shaft low, but also the height of the engine must be increased to provide the space for accommodating the balancer shafts. Moreover, it is highly possible that vibrations induced by the rotation of the balancer shafts may be transmitted to a skirt region of the engine cylinder block and then amplified to produce offensive noises and, also, it is possible that an increased number of component parts might be required which would result in the complicated and time-consuming installation of the balancer shafts.
The U.S. Pat. No. 4,497,292, patented Feb. 5, 1985, discloses the use of a lower or skirt block which is positioned between the engine cylinder block and a bearing beam structure of one-piece construction for the support of the crankshaft. Specifically, the bearing beam structure comprises a plurality of bearing caps each corresponding in position to a mating bearing recess defined in a lower block or skirt structure that is secured from below to the engine cylinder block with the crankshaft rotatably clamped between the bearing caps and the mating bearing recesses. This bearing beam structure is effective to minimize the torsional rotation of the crankshaft to thereby minimize vibrations induced by the engine system.
The support of the balancer shaft in a motor-cycle engine at the interface between the engine cylinder block and the crankcase is disclosed in, for example, the Japanese Laid-open Patent Publication No. 59-551 published Jan. 5, 1984, although no further details are clear because this publication is directed essentially to the arrangement of cylinder banks in the motor-cycle engine. However, it appears that the servicing of the crankshaft used in the motor-cycle engine disclosed in this publication requires the removal of the crankcase and that, since various bearing recesses are defined at the interface between the engine cylinder block and the crankcase, complicated and time-consuming procedures are required to re-position the crankcase, once removed for the servicing, in such a way as to permit the bearing recesses in the engine cylinder block to be exactly aligned with the mating bearing recesses in the crankcase. This problem is considerable where the engine cylinder block is made of aluminum alloy, such as disclosed in this publication, which is so relatively soft and yieldable that, when the cylinder block and the crankcase are bolted together firmly, the roundness of some of the bearings may be adversely affected.
In any event, it is well known that, even in the V-6 engine, i.e., the engine having two rows or banks of three cylinders each which banks are set at an angle to each other so as to assume the shape of a figure of "V", second-order moments tend to be generated during the operation of the engine. However, it appears that no attempt has been made to use the balancer shafts in the V-6 engine currently aboard any commercially available automotive vehicle.
More specifically, the use of the balancer shafts has originally aimed at suppressing second-harmonic vibrations occurring in four-cylinder, in-line engines in a vertical direction, suppressing moments induced in three-cylinder engine, or suppressing both of the second-harmonic vibrations occurring in the vertical direction and the moments in the four-cylinder, in-line engines. In the case of V-6 engine, since the fundamental and second-harmonic inertia forces acting in the vertical direction are substantially counterbalanced with each other and higher harmonic inertia forces can be of a substantially negligible level, it is a general notion that no balancer shaft need be installed in the V-6 engine. In addition, although it is well recognized that in the V-6 engine the second-harmonic moments tend to occur because the cylinders in one bank are offset relative to the cylinders in the other bank with respect to the direction lengthwise of the engine, no attempt has been made to use the balancer shaft or any other balancer means for suppressing the second-harmonic moments.
However, with the advent of the age of high-performance, high-quality cars, demand has been made to minimize vibrations occurring in the automotive vehicle having the V-6 engine and the presence of second-harmonic moments can no longer be negligible.